Pyrenylthioureayl Alanine as a Switch-On Fluorescent Sensor for Hg(II) Ions

Fluorescence sensing of heavy metal ion such as mercury is highly important because of its adverse effects on biological systems and on environment. Toward this end, we report herein a new and novel pyrenylthioureayl alanine amino acid (1, ^PyTUAla) as an efficient switch-on fluorescent sensor for sensing of Hg²⁺ ion in semi-aqueous solvent system (7:3 H₂O:ACN). The probe also shows binding interaction with Cu²⁺ ion with an enhancement of emission. In both the cases 1:2 metal-ligand binding stoichiometry is evident from Job's plot analyses. The detection limit is found to be 93 nM with a very high association (10¹⁰ M⁻¹) constant for Hg²⁺ ion. The UV-visible absorption, IR-spectroscopic study, NMR titration, and a theoretical calculation supported the probe's binding to Hg²⁺ ion through the coordination with two sulphur atoms of two iminothioureayl moieties of two pyrenylthioureayl alanines.